Method of manufacturing a printed circuit board including a component located in a via

ABSTRACT

A press fit passive component, such as a resistor or capacitor, adapted to fit within, or partially within, a via of a printed circuit board. In one example, the press fit passive component has a cylindrically shaped body with solderable terminals at either end of the body, and a dielectric collar disposed at least partially about the cylindrically shaped body. The component is placed in the via and soldered in order to provide a mechanical and electrical connection to the printed circuit board.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 11/969,401 filed Jan. 4, 2008, entitled “Press Fit PassiveComponent.”

FIELD OF INVENTION

The present invention relates generally to printed circuit boards andelectronic components used thereon and, more particularly, to placingcomponents within vias on printed circuit boards.

DISCUSSION OF RELATED ART

Passive components, such as resistors, capacitors and inductors, arecommonly provided on printed circuit boards as surface mount (SMT)components. Referring to FIG. 1, there is illustrated one example of astandard surface mount resistor 100. The resistor 100 has a package body102 with two solderable pads 104 for connecting the resistor to aprinted circuit board. Surface mount passive components are generallyfairly small. For example, a standard surface mount resistor, such asthat illustrated in FIG. 1, may be approximately rectangular with alength, L, of about 0.040 inches (±0.002 inches), a height, h, of about0.018 inches (±0.002 inches), and a width, w, of about 0.020 inches(±0.002 inches). However, despite the already small size of thesecomponents, the drive toward smaller and smaller electronic devices(e.g., cell phones or cameras), and thus, smaller and more denselypopulated printed circuit boards, makes placement of passive surfacemount components on printed circuit boards challenging.

In particular, one common type of printed circuit board package is theball grid array (BGA). A BGA uses an array of solder balls attached toits solderable pads on one side; it uses the solder balls to connect tothe circuit board or other substrates. Generally BGAs have very limitedspace on which to place passive components, such as resistors. Thislimited space creates a challenge for optimal component placement. Inaddition, many printed circuit boards are now multi-layer boards andtherefore, vias are used to connect surface mount components to signaltraces on other board layers as well as to the solder balls of the BGA.For example, referring to FIG. 2, there is illustrated an example of aBGA circuit board 106 with solder balls 108 making up the BGA. Vias 112a and 112 b, and traces 110 a and 110 b, are used to connect the surfacemount resistor 100 to the BGA, as shown. The trace 110 b forms an extrastub length, which can add undesirable inductance, but is required toconnect the surface mount resistor 100 to the solder ball 108 of theBGA.

FIG. 3 illustrates an example of a vertical stub caused by a viaconnecting a surface mount resistor to inner signal layers of amulti-layer board. A surface mount resistor 100 is mounted on layer one(which is the top or bottom of the circuit board) of a multi-layerprinted circuit board and connected (by its solderable terminals 104) toa signal trace 110. A via 112 is used to connect the surface mountresistor 100 to signal traces 116 on other layers. In the illustratedexample, a via pad 114 couples the via 112 to a signal trace 116 a onlayer two, thereby forming a series connection of the trace 110,resistor 100 and trace 116 a. The remaining length of the via 112 fromlayer three to the bottom via pad 118 on layer six is an extra verticalstub length that adds additional inductance and could act as an antenna.

An alternative to surface mount passive components are buried passivecomponents. With buried passive components, for example, resistors, theresistor is screened onto an inner layer of the circuit board, generallyin a rectangular area, as shown in FIG. 4. In FIG. 4, a buried resistor120 is screened onto a signal layer 122 of a circuit board and connectedto traces 116 and vias 112. Although the buried component 120 may beplaced on a inner layer, thereby possibly eliminating a via needed toconnect the component 120 from the top or bottom of the board to asignal trace on an inner layer, vias are still needed to formconnections between the signal traces on different layers. Thus, thepresence of the buried component 120 on the signal layer 122 actuallyuses up valuable via and signal trace space on the inner layers of theboard.

SUMMARY OF INVENTION

Conventional surface mount and buried passive components present severaldisadvantages to circuit board designers. Accordingly, various aspectsof the present invention are directed to an alternative form of passivecomponent, referred to herein as a “press fit passive component,” whichmay be adapted to fit within (or at least partially within) a via on aprinted circuit board. Press fit passive components may take up far lessspace on a printed circuit board than do conventional surface mount orburied passive components, and may conveniently be placed directlywithin the vias taking signals to or from board connection points, suchas the solder balls of a BGA.

According to one aspect, a press fit passive component comprises a body,collar disposed at least partially about the body, the collar comprisinga non-conductive material, a first solderable terminal disposed at afirst end of the body, and a second solderable terminal disposed at asecond opposing end of the body. The press fit passive component may be,for example, a resistor, capacitor, diode or inductor. The collar may bea dielectric material, and in one example, is a compliant dielectricmaterial. The collar may be disposed substantially about a center of thebody. In one example, the body is substantially cylindrically shaped.

One aspect of a printed circuit board may comprise a substrate having afirst surface and a second surface, the second surface being disposedsubstantially opposite and substantially parallel to the first surface,a via extending through the substrate from the first surface of thesubstrate to the second surface of the substrate, a press fit passivecomponent disposed at least partially within the via, and anon-conductive collar disposed at least partially around a circumferenceof the press fit passive component and maintaining the press fit passivecomponent within the via. In one example, the non-conductive collar isconstructed and arranged to provide a gas tight seal between the pressfit passive component and an inner wall of the via. In this example, thenon-conductive collar may comprise a C-ring. The non-conductive collarmay comprise a dielectric material. In another example, the press fitpassive component has a substantially cylindrical body and the collar isdisposed at least partially around a circumference of the substantiallycylindrical body. In another example, the printed circuit board furthercomprises a conductive trace disposed on the first surface of thesubstrate and coupled to the via, and the press fit passive componentmay comprise a solderable terminal that can be soldered to theconductive trace. In one example, the press fit passive component can becontained entirely within the via, with the solderable terminal solderedsubstantially flush with the conductive trace. In this case, a surfacemount component can be disposed above the via.

According to another aspect, a method of assembling a printed circuitboard comprises inserting a component into a via on the printed circuitboard, and soldering solderable terminals of the component to the via.This soldering may be done, for example, by wave soldering. In anotherexample, the method also includes soldering a surface mount componentover the component, and the soldering step comprises applying solderpaste to the solder terminal, applying solder paste to a pad for asurface mount component, placing the surface mount component on the pad,and soldering the surface mount component to the pad.

Another aspect is directed to a method of replacing a component locatedwithin a via of a printed circuit board. The component comprises a body,two solderable terminals and a non-conductive collar disposed at leastpartially about the body. The method comprises de-soldering thesolderable terminals of the component, and removing the component fromthe via. In one example, the non-conductive collar is a dielectriccollar, and removing the component from the via includes dissolving thedielectric collar using a chemical solvent. In another example, themethod further comprises inserting a replacement component into the via,and soldering solderable terminals of the replacement component to thevia.

Still other features and advantages of these exemplary aspects arediscussed in detail below. Moreover, it is to be understood that boththe foregoing information and the following detailed description aremerely illustrative examples of various aspects, and are intended toprovide an overview or framework for understanding the nature andcharacter of the claimed aspects. The accompanying drawings are includedto provide illustration and a further understanding of the variousaspects, and are incorporated in and constitute a part of thisspecification. The drawings, together with the remainder of thespecification, serve to explain principles and operations of thedescribed and claimed aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one embodiment are discussed below withreference to the accompanying figures. In the figures, which are notintended to be drawn to scale, each identical or nearly identicalcomponent that is illustrated in various figures is represented by alike numeral. For purposes of clarity, not every component may belabeled in every drawing. The figures are provided for the purposes ofillustration and explanation and are not intended as a definition of thelimits of the invention. In the figures:

FIG. 1 is a diagram of one example of a conventional surface mountresistor;

FIG. 2 is a diagram of one example of a conventional ball grid array(BGA) including the surface mount resistor of FIG. 1;

FIG. 3 is a vertical cross-sectional view of one example of aconventional multi-layer printed circuit board including the surfacemount resistor of FIG. 1;

FIG. 4 is a diagram of one example of a conventional buried resistor;

FIG. 5 is an exploded view of one example of a press fit passivecomponent, according to aspects of the invention;

FIG. 6 is a vertical cross sectional view of a multi-layer printedcircuit board having a press fit passive component located within a via,according to aspects of the invention;

FIG. 7 is a radial cross-sectional diagram of one example of a press fitpassive component according to aspects of the invention;

FIG. 8 is a top view of a via having a press fit passive componentlocated therein in accordance with aspects of the invention;

FIG. 9 is a perspective view of the via of FIG. 8 having the press fitpassive component located therein;

FIG. 10 is a diagram of one example of a BGA showing a press fit passivecomponent replacing a conventional surface mount component, inaccordance with aspects of the invention;

FIG. 11 is a flow diagram illustrating one example of a method ofassembly for a printed circuit board according to aspects of theinvention;

FIG. 12 is a cross-sectional diagram of one example of a printed circuitboard and underlying plate, according to aspects of the invention;

FIG. 13 is a cross-sectional diagram of the printed circuit board ofFIG. 12 illustrating another example of an underlying plate inaccordance with aspects of the invention;

FIG. 14 is a flow diagram of one example of a method of printed circuitboard assembly according to aspects of the invention; and

FIG. 15 is a flow diagram of one example of a method of reworking aprinted circuit board to replace a damaged press fit passive component.

DETAILED DESCRIPTION

U.S. patent application Ser. No. 11/969,401, filed Jan. 4, 2008, andentitled “Press Fit Passive Component,” is hereby incorporated byreference in its entirety for all purposes.

It has been found that for several types of electronic devices, forexample, some telecommunications devices, there is a need to terminatesignal traces on the printed circuit board (PCB) with a series resistorin order to match impedance of a signal source (e.g., a driver pin) tothe PCB transmission line. However, due to component spacing constraintsand limited space on the circuit board for placing resistors, addingeven one resistor to a printed circuit board design becomes difficult.Particularly, buried resistors may use up too much valuable horizontalsurface area and via space, and the use of conventional surface mountresistors may degrade electrical performance of the device due to extrastub lengths created by the vias, as discussed above. Accordingly, toaddress these and other problems with conventional passive components,embodiments are directed to press fit passive components that may belocated within (or at least partially within) vias on a printed circuitboard. A resistor placed within a via, in accordance with oneembodiment, may provide a favorable solution to the problem mentionedabove in terms of both component spacing constraints and proximity tothe location of the signal source, as discussed further below.Furthermore, according to one embodiment, press fit passive componentsmay facilitate optimizing space on a printed circuit board to facilitatedesign or more compact printed circuit boards.

It is to be appreciated that embodiments of the methods and apparatusesdiscussed herein are not limited in application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the accompanying drawings. Themethods and apparatuses are capable of implementation in otherembodiments and of being practiced or of being carried out in variousways. Examples of specific implementations are provided herein forillustrative purposes only and are not intended to be limiting. Inparticular, acts, elements and features discussed in connection with anyone or more embodiments are not intended to be excluded from a similarrole in any other embodiments. Also, the phraseology and terminologyused herein is for the purpose of description and should not be regardedas limiting. The use herein of “including,” “comprising,” “having,”“containing,” “involving,” and variations thereof is meant to encompassthe items listed thereafter and equivalents thereof as well asadditional items.

According to one embodiment, a press fit passive component is a circuitelement, such as a resistor, capacitor, diode or inductor, thatcomprises a housing, or body, designed to fit at least partially withina via on a printed circuit board, and a collar of pliable dielectricmaterial disposed at least partially about the body. Most vias onstandard printed circuit boards are cylindrical in shape. Therefore, inone embodiment, a press fit passive component may have a cylindricalbody sized to fit within a standard-sized via. For example, vias maytypically have a diameter of about 0.010 inches to 0.012 inches, andthus the press fit passive component may have a diameter slightly lessthan that range. In one example, the press fit passive component mayhave a similar, or smaller, size form factor to that of a standardsurface mount passive component. However, it is to be appreciated thatthese examples are not intended to be limiting, and that press fitpassive components according to various embodiments may have any sizesuitable for a particular printed circuit board design, whether or notthat size is the same as or similar to any standard component or viasizes. In addition, press fit passive components are not limited tohaving cylindrically shaped bodies, and may have a body that is anyshape (e.g., rectangular, trapezoidal, arbitrary, etc.) dictated only bythe application for which the press fit passive component is intended(for example, by the shape of the via or other cavity into which thepress fit passive component is to be inserted).

Referring to FIG. 5, there is illustrated an exploded view of oneembodiment of a press fit passive component 126. The press fit passivecomponent 126 includes a body 132 and two solderable terminals 130disposed at either end of the body 132. In the illustrated example, thebody 132 is cylindrical in shape; however, as discussed above,embodiments of the press fit passive component are not limited to beingcylindrical in shape. A non-conductive collar 142 is disposed about aportion of the body 132. In one example, this collar 142 comprises adielectric material. The dielectric material may comprise a pliablematerial that may be deformed under pressure, such as, for example, anelastic rubber, a polymeric material or foamed polymeric material. Byway of non-limiting example, the pliable material can bepolytetrafluoroethylene. According to one embodiment, the collar 142 maybe made of a material that provides minimal insertion force, adequatestability, can withstand high temperatures, and is still pliable enoughto close to a complete ring upon insertion. By way of non-limitingexample, the material can be a thermoset or thermoplastic polymermaterial. In addition, in some examples it may be desirable to have thedielectric collar 142 made of a material that is dissolvable (e.g.,using certain solvents) so as to allow easy removal of the press fitpassive component 126 should it be defective or incorrectly placed. Inone embodiment, the dielectric collar 142 may be placed around anapproximate center of the body 132. However, it is to be appreciatedthat other placements of the dielectric collar 142 are also possible.

Referring to FIG. 6, there is illustrated in cross-section a portion ofa multi-layer printed circuit board 124 including a press fit passivecomponent 126 inserted within a via 128, in accordance with oneembodiment. The via 128 extends through the multiple layers 134 of theprinted circuit board 124, at least some of which have signal traces 136disposed thereon. Solder 138 may be used to provide electricalconnection to the press fit passive component 126. For example, thesolder 138 may connect the solderable terminals 130 of the press fitpassive component 126 to via pads 140 which may, in turn, be connectedto signal traces (not shown) on the printed circuit board 124. Accordingto one embodiment, solder 138 may be deposited over the via 128 and viapads 140, such that it contacts the solderable terminals 130 of thepress fit passive component 126, and standard heat processes (such asthose used to solder surface mount components to a printed circuitboard) may be used to melt the solder 138 and bond the press fit passivecomponent 126 to the via pad 140, as discussed further below.

As discussed above, the press fit passive component 126 includes adielectric collar 142 disposed about at least a portion of the body 132.The dielectric collar 142 may serve to secure the press fit passivecomponent 126 within the via 128, particularly prior to soldering. Inone embodiment, the dielectric collar 142 may comprise a C-ring, asillustrated in FIG. 7. When the press fit passive component 126 isinserted (press fit) into the via 128, the C-ring may be compressed toform a gas tight seal around the press fit passive component 126. Thisis illustrated, in top view, in FIG. 8. The dielectric collar 142 maythus isolate one solderable terminal 130 from the other and preventsolder 138 from leaking through the via 128 and “shorting out” the pressfit passive component 126.

According to one embodiment, the via 128 may include conductive plating(not shown) along a portion of the via sides, for example, extending asfar down the via as to reach the solderable terminals 130 of the pressfit passive component 126. However, the via 128 should have noconductive plating along at least an interior portion, for example, thearea approximately corresponding to the location of the dielectriccollar 142, so as to prevent a short circuit from being formed acrossthe press fit passive component 126. According to one embodiment, CAD(computer aided design) software can be designed to accommodate pressfit passive components. In particular, the CAD software can be adaptedto allow placement of a press fit passive component 126 within a via128, and to specify plating of the via only on certain layers (such asthe top and bottom layers, but not some inner layers).

Press fit passive components according to various embodiments mayprovide several advantages to printed circuit board designers andmanufacturers. For example, by using press fit passive componentslocated within vias, a printed circuit board designer may no longer needto add the extra vias and traces that were required to connect a surfacemount component to appropriate signal traces (as shown in FIG. 2).Rather, referring to FIG. 10, a press fit passive component (not shown)may be placed directly in the via 112 b that takes the signal from theBGA to the inner layers, obviating the need for the traces 110 a and 100b and the extra via 112 a. Reducing the number of vias may decrease thecost of the printed circuit board and free up more space for signaltraces. Furthermore, the press fit passive component takes up limitedhorizontal space on the printed circuit board, in one example, far lessspace than is used by conventional surface mount passive components(such as resistor 100) or buried passive components. For example, aconventional surface mount resistor of the 0402 size, together with itsvias, takes up approximately 2400 sq. mils of surface area, whereas apress fit passive component would require only the surface area of thevia in which the component is located, which is about 576 sq. mils.Accordingly, a press fit passive resistor can provide approximately 75%savings in board surface area compared to a conventional surface mountresistor. Thus, press fit passive components may save considerablecomponent space on the printed circuit board and facilitate theproduction of higher density printed circuit boards. In addition,elimination of via 112 a and traces 110 a and 100 b will also eliminatethe vertical stub (see FIG. 6) before the signal reaches the resistor.As discussed above, these vertical stubs cause unwanted inductance andcan act as antennas, which can degrade the electrical performance of theboard. Therefore, removal of these vertical stubs can be advantageous,particularly for high-speed devices, such as, for example,telecommunications devices.

According to one embodiment, a method of producing a populated printedcircuit board may include placing a press fit passive component on theprinted circuit board before or during the process of populating theboard with other active and/or passive surface components. Referring toFIG. 11, there is illustrated a flow diagram of one example of such amethod. It is to be appreciated however, that the order of stepspresented in FIG. 11 is one example only and not intended to belimiting, and that embodiments of methods of assembling printed circuitboards may use more or fewer steps than, or may be otherwise modified ascompared to, those illustrated in FIG. 11, and may implement those stepsin an order different to that shown in FIG. 11. In some applications, itmay be currently preferable to place any press fit passive components onthe printed circuit board before other surface mount components areplaced. Thus, a first assembly operation on the printed circuit board(step 200) may include placing the press fit passive components on theprepared printed circuit board. However, it is to be appreciated thatthis need not be the case, and other components may be placed (andoptionally soldered) before placement of press fit passive components onthe printed circuit board. It is further to be appreciated that “pressfit passive components” as used herein is intended to refer to one ormore press fit passive components.

Conventional surface mount components are generally supplied in reelsthat are fed into a component dispensing machine. The reels hold thediscrete components in such a manner that the dispensing machine can beeasily fed. Similarly, in one embodiment, press fit passive componentsmay be supplied in reels that may be fed into a dispensing machineadapted to accommodate press fit passive components. For example, thedispensing machine may include a press-fit insertion tool that may takea press fit passive component from the reel and press the component intoa prepared via on the printed circuit board.

In one embodiment, a fixture may be used to hold the printed circuitboard stationary while the press fit passive components are insertedinto prepared vias. In conventional assembly of printed circuit boardshaving surface mount components, mechanical fixtures are used to holdthe printed circuit boards as the boards are moved from one dispensingstation to another and the components are placed on the board.Therefore, the same, or a similar, fixture may be used to hold theprinted circuit boards during placement of the press fit passivecomponents. A plate made of a substantially inflexible substance may beplaced under the printed circuit board and pressed flush to the printedcircuit board from the bottom of the board. This plate may prevent thepress fit passive components from being pushed through the printedcircuit board. A press-fit insertion tool may be used to press thecomponent into the printed circuit board. The press-fit insertion toolmay be controlled to exert sufficient force on the press fit passivecomponent so as to insert it without damaging the press fit passivecomponent. In one example, the press-fit insertion tool may becontrollable (e.g., by way of a user interface) so as to adjust theinsertion force based on, for example, the material used for thedielectric collar on the press fit passive component.

In some applications, the press fit passive component may extend outfrom the via above one or both of the top and bottom surfaces of theprinted circuit board. In such instances, the underlying plate may haveholes formed therein that correspond to the locations of the viasthrough which the press fit passive component(s) may extend. Referringto FIG. 12, there is illustrated a printed circuit board 144 having aplurality of vias 128 (at least some of which may receive press fitpassive components) formed therein. A plate 146 is held against thebottom surface of the printed circuit board 144 by the fixture, aportion 150 of which is schematically illustrated in FIG. 12. The plate146 has a plurality of holes 148 formed therein, as discussed above. Inone example, as illustrated in FIG. 12, the holes 148 are shown as beingslightly larger than the vias 128, and thus larger than the press fitpassive components, in order not to damage the press fit passivecomponents. However, it is to be appreciated that the holes 148 may beformed having substantially the same size as the vias 128, or may belarger than the vias. It will be appreciated that the location of vias128 on different printed circuit boards 144 can be different. Therefore,in one example, each type of printed circuit board 144 may have acorresponding plate 146 having holes 148 precisely drilled (or otherwiseformed) therein to correspond to the locations of the vias 128.

Alternatively, as shown in FIG. 13, rather than having multipleprecisely located holes 148, the underlying plate 146 may have arecessed surface 152 that may correspond to a majority of the surfacearea of the printed circuit board 144 (but leaving a rim around therecessed surface to allow the plate 146 to be clamped to the printedcircuit board 144). Having this recessed surface 152, rather than aplurality of precisely located holes 148, may allow one plate 146 to beused for multiple different printed circuit board layouts. The depth ofthe holes 148 (or recessed surface 152) may be dependent on the heightof the exposure of the press fit passive component from the surface ofthe printed circuit board 144. Therefore, in one example,controlled-depth-drilling may be used to form the holes 148 (or recessedsurface 152) to a desired depth.

As discussed above, press fit passive components may be provided inreels, similar to conventional surface mount components. In one example,the placement of the press fit passive component in the reel may definethe polarity direction of the press fit passive component, top or bottomon the printed circuit board 144. If all of the press fit passivecomponents were designed to have one type of polarity, either negativeor positive on the top of the board, the press-fit operation may be donein one step. Alternatively, if some press fit passive components have anopposite polarity to others, the board 144 may be flipped (e.g., byrotating the fixture) over to the opposite side for a second press-fitoperation. Rotating fixtures are known in the art and are commonly usedwith surface mount component dispensing machines that do not haverotatable dispensing heads, in order for the non-rotatable dispenserheads to account for the direction of the polarity of the component onthe printed circuit board 144. The rotating fixture may also accommodateintegrated circuits (ICs), which may be rotated in different directions.Accordingly, in at least one example, such an existing fixture, or amodification thereof, may be used to hold and rotate the printed circuitboard 144 during placement of the press fit passive components. When theboard 144 is flipped, the underlying plate 146 may be moved from oneside of the board to the other, or the plate may be removed and anotherplate attached to the new underside of the board. In some conventionalmanufacturing operations, the dispenser may have a rotating head thatwill rotate to account for the direction of the polarity of thecomponent on the printed circuit board 144. Therefore, in at least oneexample, the dispenser/insertion tool for press fit passive componentsmay have a rotating head, thus obviating the need to rotate the printedcircuit board 144 with the fixture. Alternatively, a reel of press fitpassive components with the opposite polarity may be provided and loadedinto the dispensing machine/insertion tool.

Referring again to FIG. 11, after placement/insertion of the press fitpassive components is complete, the press fit passive components may besoldered in place (step 202). In one example, a technique generallyknown in the art as wave soldering may be used to implement this step.Alternatively, a solder dispensing tool may be used to apply solderpaste to the solderable terminals of the press fit passive component(s)on one side of the board 144. In this case, step 202 may also includeapplying solder paste to the solderable pads of any surface mountcomponents that are to be placed on that side of the printed circuitboard 144. The printed circuit board 144 may then be placed in clamps ona conveyor belt (step 204). The conveyor belt runs past multiplestations where mechanical dispensers press any surface mount componentsonto the board 144. Of course, if there are no surface mount componentsto be added to the printed circuit board 144, the method may skip step204. Next, the board 144 may be sent to an infrared (IR) oven where thesolder paste is melted, creating a solder joint (step 202). Thisprocedure may then be repeated for the opposite side of the board (step208).

As discussed above, in some examples, press fit passive components mayextend from the via 128 above the surface of the printed circuit board144. According to another embodiment, press fit passive components maybe designed to fit entirely within a via 128, such that the componentmay fit below the surface of the printed circuit board 144. In thiscase, the press fit passive component may be soldered flush with thesurface of the printed circuit board 144. Then, surface mount componentsmay be placed over soldered-in press fit passive components. In oneexample, the body of the surface mount component may be placed above thepress fit passive component, with its solderable pads being on eitherside of the press fit passive component. This arrangement may avoid theneed to solder on top of an already existing solder joint (i.e., thesolder joint connecting the press fit passive component to the via pad).

In another example, the press fit passive component may be placedunderneath a solderable pad for surface components such as gull wing,j-leaded or quad-pack devices. In another example, the press fit passivecomponent may be located directly beneath a solder ball of a BGA. Inthis case, the assembly process may include a step of soldering thesurface mount components to the pre-existing solder joints. Such “doublesoldering” may be accomplished, for example, by using a highmelt-temperature solder paste to solder the press fit passivecomponents, and then using a lower melt-temperature solder to solder thesurface mount components. The difference between the twomelt-temperatures for the different solder compounds may allow thesurface mount components to be soldered on top of the press fit passivecomponent solder joints without melting the existing joints.Alternatively, a method may include electrical or chemical plating overthe ends of the press fit passive component. Surface mount componentsmay then be soldered or otherwise attached to the plating.

The ability to mount surface mount components above press fit passivecomponents may provide a substantial savings in component space on theprinted circuit board since the press fit passive component would takeup no surface area on the board. However, even in embodiments in whichthe solderable end(s) of the press fit passive component protrude out ofthe printed circuit board on either or both sides, the press fit passivecomponent may still take up far less horizontal surface area on theboard than do conventional surface mount devices. Thus, press fitpassive components may provide a substantial advantage to printedcircuit board designers and manufacturers by reducing component surfacearea, which may allow smaller and/or more densely populated circuitboards to be produced.

After the assembly process takes place, the printed circuit board may betested for any faults prior to packaging and shipment to a customer.According to one embodiment, installed press fit passive components maybe tested before other components are installed on the printed circuitboard. Thus, referring to FIG. 14, in the board assembly method flowdiagram, a step 210 of testing the press fit passive components may beincluded prior to placement of any surface mount components. Where thesolderable terminals of the press fit passive component are exposed(e.g., the press fit passive component extends above the surface of theprinted circuit board or, even if the press fit passive component issoldered flush with the printed circuit board, no component is placedabove it), the press fit passive component may be easily tested with aclamshell tester or by probing from both sides of the printed circuitboard simultaneously. However, if the press fit passive component isplaced underneath a surface mount component pad (i.e., is concealed),other methods of testing may be required. For example, the concealedpress fit passive component may be tested using x-ray technology. X-raytesting is currently preferred if, for example, the press fit passivecomponent is placed between two surface mount devices located on the topand bottom surface of the printed circuit board. Alternatively, a thinwire may be guided, using a theoretically guided program, underneath thesurface mount component to a designated pin on either side of theprinted circuit board simultaneously so as to test the press fit passivecomponent.

According to one embodiment, if a press fit passive component fails, forexample, or is cracked from the insertion force and/or exposure to hightemperatures (e.g., during soldering), then a rework process may beimplemented to replace the component. Referring to FIG. 15, there isillustrated a flow diagram of one example of a rework process to replacea press fit passive component. The steps in the rework process may varydepending on whether or not the press fit passive component is locatedbeneath a surface mount component, as indicated by block 212.

If the press fit passive component is not underneath a surface mountdevice, each side of the press fit passive component may be easilyde-soldered (step 214). This de-soldering may be accomplished usingtools and techniques known in the art. After the press fit passivecomponent has been de-soldered, it may be removed from the via (step216). As is currently preferred, removal of the press fit passivecomponent may be achieved without damaging the printed circuit board. Ifthe press fit passive component is located underneath a surface mountpad, the surface mount device would have to be removed first. Removal ofthe surface mount component (step 218) may be achieved usingconventional tools and techniques, as known to those skilled in the art.

According to one embodiment, a tool for removing press fit passivecomponents may include a shaped piece of metal with a hole in the centerto support the bottom of the printed circuit board, and a punch thatwould push the press fit passive component out of its via. In oneexample, the shaped piece of metal may be cylindrical. If only a fewpress fit passive components need to be removed, the tool may beimplemented as a hand tool. Alternatively, to accommodate removal ofmany press fit passive components, the printed circuit board may be heldstationary in a fixture, and a computer driven machine may manipulatethe tool to remove the press fit passive component. For example, themachine may manipulate the cylindrical metal piece both vertically andhorizontally under the printed circuit board in unison, with the punchon either the top or bottom of the printed circuit board.

According to another embodiment, removal of the press fit passivecomponent may include dissolving the dielectric collar, for example,using a chemical solvent. As discussed above, the dielectric collar mayserve to secure the press fit passive component within the via.Therefore, when the dielectric collar is dissolved, the press fitpassive component may be more easily removed from the via.

Referring again to FIG. 15, after removal, a failed press fit passivecomponent may be replaced by inserting a new press fit passive componentinto the via and soldering the solderable terminals (step 218). Ifappropriate for the design, the same (or a new) surface mount componentmay be soldered above the press fit passive component (step 220), forexample, by using the double soldering and/or plating techniquesdiscussed above.

Having thus described several features of at least one embodiment, it isto be appreciated various alterations, modifications, and improvementswill readily occur to those skilled in the art. Such alterations,modifications, and improvements are intended to be part of thisdisclosure and are intended to be within the scope of the invention.Accordingly, the foregoing description and drawings are by way ofexample only, and the scope of the invention should be determined fromproper construction of the appended claims, and their equivalents.

1. A method of assembling a printed circuit board (PCB) having first andsecond electrical pads on first and second opposed surfaces,respectively, the PCB having at least one via running from the firstsurface through the PCB to the second surface, the method comprising:providing a component comprising: a passive electrical device havingfirst and second ends and an outer diameter; first and second solderableterminals, each having a respective outer diameter, mechanically andelectrically coupled, respectively, to the first and second ends of thepassive electrical device; and a non-conductive collar disposed at leastpartially around and partially along a length of at least one of thepassive electrical device and the first and second solderable terminalsand having an outer diameter that is greater than the outer diameters ofthe passive electrical device and the first and second solderableterminals; inserting the component into the at least one via; andelectrically coupling the first and second terminals of the component tothe first and second electrical pads, respectively.
 2. The method asrecited in claim 1, wherein the passive electrical device is one of aresistor, a capacitor, a diode or an inductor
 3. The method as recitedin claim 1, wherein the collar comprises a dielectric material.
 4. Themethod as recited in claim 3, wherein the dielectric material is acompliant material.
 5. The method as recited in claim 1, wherein thecollar is disposed substantially about a center, length-wise, of thepassive electrical device.
 6. The method as recited in claim 1, whereinthe passive electrical device is substantially cylindrically shaped. 7.The method as recited in claim 1, wherein electrically coupling thefirst and second terminals of the component comprises: soldering thefirst terminal to the first electrical pad and creating a first solderjoint therebetween; and soldering the second terminal to the secondelectrical pad and creating a second solder joint therebetween.
 8. Themethod as recited in claim 7, further comprising: soldering a solderball of a Ball Grid Array (BGA) device to one of the first and secondsolder joints.
 9. The method as recited in claim 8, wherein: creating atleast one of the first and second solder joints comprises soldering witha solder paste having a first melting temperature; and soldering thesolder ball comprises soldering with a solder paste having a secondmelting temperature lower than the first melting temperature.